One small tip for your readers : in order to display the content differently through common devices, we design some prototypes and go outside, showing them to our audience in real life. It allows us to understand what our users want and what’s the most important for them.

At first I didn’t got the point of designing for different widths, I always made a design for mobile and a design for desktop.

But it is indeed right what you say. You can’t know what the next big thing will be and what the resolution of that device will be. With a responsive design you make sure that the website design will be longterm.

This article contains some very good tips to make a responsive design work.

Good article. But I disagree with your opening statement about Response Design, “The most important part of responsive web design is that, no matter what the viewport width”. Width is not just one aspect of Response Design, it is a single conditional (just like touch events and other browser/device capabilities). The most important part of Responsive Design is user experience, that’s why it exists — to meet the context or mindset of the user by providing the optimum experience not dependent of their browser capabilities or limitations.